Because so many of the images in this book are taken from high orbits and are often taken at oblique angles, scale changes widely within most of the images. A scale bar would be misleading. Consequently, care has been taken to identify the diameter of a few features within each image.
The diameter and age of many features are given in a "key" table that accompanies the notes of each annotated image. The diameter is usually taken from the IAU catalog. The diameter of basins is as given by the USGS (Wilhelms, 1987). In some cases, these diameters differ slightly from the IAU diameters when a basin coincides with a named feature, but the USGS diameter is always used for basins, for consistency.
The age period assigned to features is also taken from the USGS (color plates of Wilhelms, 1987). An attempt has been made to include all features named in these plates in the keys, as well as some features identified, but not named, on the plates.
The Western Far Side Region: Earth-Rise, Tsiolkovskiy, Gagarin, and the Mendeleev Basin c o o 3E
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